Paul McCartney has revealed a bizarre fact about The Beatles' icon Sgt. Pepper's Lonely Hearts Club Band album - a sound only dogs can hear features on track 'A Day in the Life'.

Whilst speaking to Zane Lowe about vinyl (which he thinks is "the best"), McCartney said: "I asked my engineers whilst (vinyl) sounds good and they explained there are frequencies above and below that you can't hear." He continued: "We'd talk for hours about these frequencies below the sub that you couldn't really hear and the high frequencies only dogs can hear. We put a sound on Sergeant Pepper only dogs can hear. If you ever play Sergeant Pepper watch your dog." The high pitched whistle can be found on the final track on the album, 'A Day in the Life', which is named by many as the band's best song. Who knows, your dog may even become a fan, as the high frequency 15 kilohertz sound can be detected by canines but not the human ear.